Forcing "POSIX 1003.1-2001 with XSI" removes locale_t from <locale.h>.
This breaks including libintl.h, since gettext is built with locale_t
in view.

Index: src/Makefile.in
--- src/Makefile.in.orig
+++ src/Makefile.in
@@ -377,7 +377,7 @@ tpad_SOURCES = \
 	tpad_open_guard.c \
 	tpad_open_guard.h
 
-tpad_CFLAGS = -D_XOPEN_SOURCE=600 
+tpad_CFLAGS = 
 tpad_LDFLAGS = 
 tpad_LDADD = $(TPAD_LIBS) \
 	-lpthread \
